Oxygen absorbent media



m R T N 0 F M Q OXYGEN ABSORBENT MEDIA 3 Sheta-Sheet 1 Filed Aug. 7,1944 ER Y mm m m J/ w 0 a w W, W48. c. M. FONTANA 2,447,323

OXYGEN ABSQRBENT MEDIA Filed Aug. 7, 1944 3 Sheets-Sheet 3 RAZTZ' OFCEORIMTION 0F AIETHANE I o 7 3 a mw I 01'" com SALT AS CUPRIC' CHLORIDE1N MELT WYTH J0 MOL XC'l Celesie M Fbniana F] J INWVTOR A TE'URNE Y'ods' are intrinsically oi oxygen absorption.

Patented Aug. 17, 1

OXYGEN ABSORBENT MEDId Celeste M. Fontana, Dallas. Tern, assignor, bymemo cuts, to Socony-Vacu Gil Company, Incorporated, N York, N. EL, acorporation oi New York Application 1 31"" 7, 19%, Serial No. 548,349

1 claim. (or. 252-189) K This invention relates to a method ofextracting oxygen from the air by the use of molten salts comprising thechlorides of copper in admixture with alkali metal halides, especiallyalkali metal chlorides such as postassium chloride. More particularlythe invention is concerned with the preparation of'melt mixtures ofcopper. chlorides and'potassium chloride in concentrations so adjustedthat the melting points of such mixtures are suflicieutly low thatoxygen may be absorbed from the air by the liquid melts as hereinafterdescribed and as described in greater detail in U. 8. Patent 2,418,402.The invention is also concerned with the preparation of such melts forutilization in the process of making chlorine and chlorinatedhydrocarbons as described and claimed in U. 3. Patents 2,407,828,2,418,930 and The present invention concerns the optimum concentrationsof the chlorides of copper and of potassium chloride in said melts toobtain high, rates of oxygen absorption from the air, and also toproduce melts which are liquid at temperatures of operation 'of thevarious steps of the processes, thereby making possible continuouscyclic "operation.

Numerous methods have been proposed in the prior art for the preparationof oxygen from air.

These methods'maybe classified as those involving Physical methods ofseparation such as liquefaction followed by fractionation of the liquidair and those involving chemical methods such as absorption anddesorption of oxygen by'chemical metals which were then desorbedofoxygen either at elevated temperature or reduced pressure. These methodsproved cumbersome in practice and in the case of barium oxide (Brinsprocess) required relatively pure air with respect to carbon dioxidecontent. He'nce liquefaction methodsv were later adopted. However,liquefaction methexpensive involving costly high pressure refrigerationequipment. The present inventionrelatesto a chemical method adaptablefor continuous'production of oxygen from ordinary air by employing meltsof copper chlorldes with alkali metal chlorides in such proportions' asto give liquid ior maximum rate The most widely used method forproducing chlorine is the electrolytic method. Other meth" odsinvolvethe recovery of chlorine from hydrogen chloride. The prior artemployed. in general, two methods for converting hydrogen chloride tochlorine; The first method involves direct catalytic oi'iidation ofhydrogen chloride to chlorine. Common among the catalysts employed havebeen copper halides supported on porous materials such as pumice.Promoted copper cata lysts having some other substance added to im provetheir catalytic activity have also been pro posed. Addition agentssuggested as efiective are oxygen compounds of vanadium, beryllium,magnesium, bismuth, antimony, uranium and rare earth metal compounds.These catalytic processes all suffer from the same disadvantage, via,the products from the catalytic converters require diflicult andexpensive treatment in order that quantitative yields of pure chlorinebeoh tained.

The second method proposed in the prior art for the production ofchlorine is a cyclic two stage process, involving in the first stage,ahs'orption of-the hydrogen chloride in a metal oxide, whereby the metaloxide is converted to the chloride, and, in the second stage, thereconversion of the metal chloride to the oxide and chicrine by means ofoxygen at a higher temperature. The "Mond process is a typical exampleof such a process in producing only a dilute chlorine containing gas andhaving the additional disadvantage of the necessityof alternatelycooling and heating a stationary mass in the converter over aconsiderable temperature range while changing over from one stage of theoperation to the other, resulting in heat losses and inefficient use ofthe converter during the heating and cooling operations. As in the caseof a more eflicient method for producing oxygen, the present inventionsupplies. a medium for, oxygen absorption and heat transfer thus makingpossible a continuous cyclic process for producing chlorine.

A third process to which my invention is an important contribution isthat of recovering hydro gen chloride in the form of alkyl halides suchas methyl chloride described in detail in the hereinabove mentioned U.S. Patent 2,407 ,828. Hydrogen halidesysuchas hydrogen chloride,are-liberated, in the production of alkyl halide intermediates byhalogenation of hydrocarbons and in the conversion of such halides tothe final products; hence the commercial feasibility of "these processesusually depends upon the economical recovery of the halogen acids andtheir reconi accuses methane are carried out simultaneously. Forexample, it has been suggested that methyl chloride be produced bypassing a mixture of methane, hydrogen chloride and air, or oxygen, overa supported copper halide catalyst. In the use of metho'ds involvingsimultaneous oxidation of hydrochloric acid and chlorination ofhydrocarbons, particularly methane, the yields of chlorometnlines arelow and considerable hydrogen chloride passes through the converterunchanged and the chloromethanes are highly diluted with water vapor andair, thus requiring additional and expensive processing'to obtain theohloromethanes in purified form.

A primary object of the present invention is to provide melts of copperchloride with alkali metal halides, preferably with potassium chloride,for

' utilization as absorbent media for oxygen in improved continuousoyclic processes for the production of oxygen, and for the production ofchlorine or chlorinated hydrocarbons from hydrogen chloride involving anoxidation step.

A further object of the invention is to provide melts oi the chloridesof copper with potassium chloride in such proportions that maximum ratesof absorption of oxygen from the air can be obtained at operatingtemperatures adaptable to improved methods oi? producing oxygen,chlorine or chlorinated hydrocarbons.

An additional object of this invention is to produce a carrier supportedmixture of chlorides of copper and potassium chloride in suchproportions of potassium chloride to copper chlorides that the heatedmixture of chlorides will show high rates of oxygen absorption.

Still another object of the invention is to produce oxygen absorptionmelts of copper chlorides with potassium chloride in proportions suchthat said melts may be readily maintained in the liquld phase in all ofthe steps and transfer-operations in the methods referred to above forproducing oxygen. chlorine, or chlorinated hydrocarbons. j

Other'and further objects of the invention will be apparent from thedescription thereof and from the appended claims. v

Cuprous chloride may be converted to the cupric oxide-cuprlc chloridecomplex form by reacting the molten chloride with air according to thefollowing equation:

If it is desired to recover hydrogen chloride by reconversion tochlorine. the molten mass containing oxychloride is contacted with thewaste gas containing the m'drogen chloride and reaction takes placeaccording to the equations:

If on the other hand it is desirable to utilize the chlorine directly toproduce alkyi chlorides such pressed by the equation: (5) CH4+2CuCl 2-CHsCl+2CuCl+I-IC1- As described in detail hereinbel ow, I haveillustrated my process atically in Figure 1 wherein is shown theapplication of the copper chloride-potassium chloride melts in a.process for converting hydrogen chloride to alkyl chlorides using copperchloride-potassium chloride melts in optimum concentration of potassiumchloride, cuprous chloride and cupric chloride. The process incorporatesthree successive steps wherein the principal reactions occurring in thesteps are illustrated by Equation 1, Equation 3 and Equation 5respectively. The first reaction zone is designated as the preoxidationzone, the next zone is designated the oxidation-neutralization zone andthe final zone, the chlorination zone,

Since it is desirable to maintain the melt in a liquid state in theoperation of a continuouscyclic process, the choice of composition ofthe melt to be used is determined (1) by the freezing point of the meltasafi'ected by change of composition relative to proportions of cuprouschloride and cupric chloride in successive steps of the process and bythe mole percent of potassium chloride in the melt, (2) by the desiredrate of oxidation of the melt, and (3) by the desired rate ofchlorination by the melt.

It has been found that potassium chloride as a third component inadmixture with cuprlc and cuprous chlorides produces melts of relativelylow freezing points and other suitable properties, and

hence is a desirable component in such a mixture for reducing tocontinuous cyclic operation processes involving the use of thesecomponents such as for the production or oxygen. for the oxidation oforganic materials, for the production of chicrine and for thechlorination .of hydrocarbons. I have found that in addition toproducing relatively low freezing point melts of copper chlorides,potassium chloride at optimum concentrations greatly increases the rateof oxidation of cuprous chloride in the melt. I have further found thatthese optimum concentrations with respect to rate of oxidationcorrespond very closely to minimum melting compositions of the copperchloride-potassium chloride mixtures.

Potassium chloride occupies a unique position as a third component inregard to freezing point depression of the copper chloride salts. Sodiumchloride as a third component does not give a comparable lowering, but apart of the potassium chloride in the melt can be replaced by sodiumchloride or other alkali metal chlorides without appreciably alteringthe extent of .the lowering. Thus crude potassium chloride containingappreciabie amounts of other alkali metal halides can be used, theeffect of such impurities being to further lower the freezing points.

I have found that melts suitable with respect to both freezing point andrate of oxygen absorption contain from 20 to 50 mole percent potassiumchloride, the preferred range of potassium chloride content being from25 to 45 mole percent. The basis for the above preferred limits willbecome clear in the subsequent discussion and by reference to Figure 2.

' Cupric chloride forms a complex or the composition KzCllCh with thepotassium chloride of the melt. As a first approximation it can beconsidered that the melt after it has been used for chlorination oroxidation will be approximately a mixture ot'iiux of cuprous chloride inKaCuCh. Such a mixture is to be understoodas included in the ternarysystem cuprous chloride, cupric chloride and potassium chloride. Forexample, a mixture consisting of 30 mole percent potassium chloride,mole percent cupric chloride and 55 mole percent cuprous chloride is tobe considered identical witha mixture consisting of 55 moles cuprouschloride, CuCl, and 15 moles of the complex 'KzCuCh or a mixturecontaining 78.6 mole percent of cuprous chloride and 21.4 mole percentof the complex KzCuCh. The for-- mation of this complex causes a part ofthe cupric chloride to remain practically inactive for chlorination asshown in Figure 3 wherethe rate of chlorination of methane in arbitraryunits is plotted against percent of the copper in the cupric chlorideform for a melt containing 30 mole percent K01."

However, it may also be seen from-Figure 8 that at higher temperaturesthe said complex begins to show some activity. For example, the 400' C.chlorination rate curve may be extrapolated approximately as a straightline to zero chlorination rate at the point where 21.4 mole percent ofthe copper salt is cupric chloride which represents the cupric chlorideftied up as inactive complex, KzCllCh. On the other hand thechlorination rate curves at higher temperature deviate from a linearrelation in the neighborhood of 21.4 percent cupric chloride, thedeviation being greater the'higher the temperature. This shows that thecomplex KrCuCh becomes more active at higher temperatures as a result ofpartial thermal decomposition into free cupric chloride and freepotassium chloride. Therefore, I do not wish to be restricted tooperation in the range of percent cupric chloride in excess of thatrequired to form the complex KzCuCh.

In view of the approximate limitation of activity of cupric chloride bythe formation of the complex K'iCuCh, I have determined rates ofabsorption of oxygen as a function of mole percent of potassium chloridealong a line corresponding to mixtures of potassium chloride withKcCuCh. The results are shown in Figure 2 wherein the rate of oxidationat 400 0., ex-' pressed in arbitrary units, is plotted against molepercent of potassium chloride in the melt. From the curves in Figure 2it is clear that a maximum rate exists. Also in Figure 2, are plottedthe allowable ranges of cuprous chloride change as a function of molepercent potassium chloride at various temperatures, the range at anypoint being limited on the one hand by the freezing point of the meltand on the other by the inactivity of somewhat active at the highertemperatures. is seen that for temperatures between 300C.

- a melt will be in liquid form at temperatures 'KzCllCh, which aspointed out before becomes and 450 C. a maximum change in cuprouschloride content is possible for melts containing from 25 to 45 molepercent potassium chloride. It may thus be seen that the preferredpotassium chloride content with respect to both rate of oxygenabsorption and freezing point is from about 25 to 45 mole percent withthe outer limits from about 20 to about 50 mole percent potassiumchloride.

In making up my copper chloride-potassium chloride melt, I may introducefresh melt havingv a composition approximately 30 to 35 mole percentpotassium chloride, and to 65 mole percent chlorides of copper of whichapproximately 1 15 mole percent consists of cupric chloride and aboveabout 250 C. and the mixture will remain in liquid form even 1 though inthe oxidationneutralization step. therelative concentration of cupricchloride to cuprous chloride'may change from an initial ratio or 15:55to a ratio as high as 50:20 since the temperature of the melt mixtureincreases, as a result 'of the exothermic character oi the oxidationreaction, to 450 C. or even 500 C. in that part of the reactor wherethese higher concentrations of cupric chloridepredominate. Thefreezing'point oia melt having a composition of 50 'mole percent cupricchloride, 20 mole percent cuprous chloride and 30 mole percent potassiumchloride is about 430 C.

The above ratios of cupric chloride-to cuprous chloride should not beinterpreted as limitations on the melt composition. In fact, the onlynecessary specification i'or making up the melt for the chlorinationprocesses is on the ratio of potassium chloride to copper chlorides,since the ratio of cupric chloride to cuprous chloride in themeltchanges in use. For example, in the process described below, regardlessof whether the starting melt contains substantially all of the copperchloride in the cupric form or substantially all of the copper chloridein the cuprous form, the range of ratios of cupric'chloride to cuprouschloride present in the melt for on stream operation will assume thesame values,

which values will depend somewhat on the operating conditions. Thesevalues of mole ratios I of cupric chloride to cuprous chloride forcontinuous on stream operation will lie within the range of from about1:10 to about 10:1.

I do not wish to be restricted to the circulation of the liquidmoltensalt mixtures per se since the preferred compositions may beabsorbed or impregnated on suitable inert porous supporting materialsand circulated by any of thewell known "fluid." techniques. Suchmaterials as alumina, alumina gels, silica gels, alumina-silica gels,tull ers earth, ini'usorial earth, pumice, kieselguhr, etc, may beemployed. These carrier materials may be impregnated with the saltmixtures by any of the well knownmethods but preferably by absorption ofthe salts from a concentrated aqueous solution, for example, aconcentrated solution of cupric chloride and an alkali metal chloridesuch as potassium chloride containing the preferred ratio 20 to 50 molesof alkali metal chloride to moles total of the two salts. Where thechlorides are supported on inert carriers freezing point considerationsare not controlling and hence, any alkali metal chloride may be used tomodify the rate of reaction.

The material after filtration and drying may be crushed. If theimpregnated carrier is to be suspended in a gas such as in air for theproduction of oxygen as described and claimed in copending application.Serial No. 548.350. filed August 7, 1944, by Edwin Gorin and applicant,the particle size of the crushed impregnated carrier so used will bewithin the range of 10 mesh and 10 micron size, preferably within therange-of 30 mesh and 50 micron material. The impregnated carrier may beused for chlorination or if it is to be used for voxygen absorption asdescribed above, the cupric chloride content is first partially reducedto cuprous chloride, for

' example, by contacting with a hydrocarbon at amass:

' solid at temperatures above the melting point of the supported mixtureof chlorides.

In order to illustrate specifically the manner in which my novel saltcomposition may be prepared for use as a carrier impregnated reactant,0.70 mol of cupric chloride and 0.30 mole of potassium chloride weredissolved in water to form 250 cubic centimeters of solution. Thesolution was added to finely pulverized i'nfusorial earth to form aslurry. The material was filtered and the solid was dried at 150 C. andvpulverized. The anhydrous powder contained 23.6 weight percent of cupricchloride salt and 5.6 weight percent of potassium chloride. Theimpregnated powder was heated to 500 C. without agglomeration and wasshown to react in a manner analogous to a 30 mole percent potassiumchloride melt except for a greatly accelerated rate of reaction due tothe extent of exposed surface. The cupric chloride was partially reducedin situ by contacting the mass with methane at about 410 C. and theresulting powder was found to absorb oxygen rapidly from a stream of airin a temperature range from 300 C. to 450" C. After contacting the oxidecontaining powder with hydrogen chloride the powder was used tochlorinate methane in the temperature range from 350 C. to 525 C. Therate of chlorination was rapid at temperatures above about 375 C.

In order to illustrate the manner in which the improved copper chlorideoxygen absorbent melts may be used, the following description of anadiabatic process for the chlorination of methane is given in connectionwith Figure 1.

Referring to Figure l, a molten mixture consisting of about 30molepercent potassium 'chloride, 55 mole percent of cuprous chloride andmole percent cupric chloride is introduced at a temperature within therange of from about 350 C. to about 400 C. through line it and pump Iito packed preoxidizer tower l2 where it is contacted with air introducedto tower l2 by means oi compressor II in line I3. I prefer to operatethe preoxidation tower at pressures above atmospheric, pressures as highas or atmospheres being suitable for this operation.

The function of the preoxidation step is to produce a part of theunstable oxychloride. CuO-CuCla in a zone ahead of theoxidationneutralization step in order to supply an absorbent for anyhydrogen chloride present near the top 01' the oxidation-neutralizationtower described below. Fresh cuprous chloride melt or recycle cuprouschloride melt containing either free cupric chloride or the complexKaCllCh coming in contact with water vapor in the eiliuent as from theoxidation-neutralization tower i1 hydrolyzes to a certain extent to formHCl. Hence, recycle cuprous chloride is first partly converted to theoxychloride in the preoxidation tower before entering tower II. Anadditional function of the preoxidizer is to heat up the main air streampassing as overhead from preoxidizer 12 through lines l5 and valvedlines Ito, lib and lic to the oxidizer-neutralizer II. By the properadjustment of the valves in line I! and by-pass line II, I may by-passthe preoxidizer I! with a part of the necessary air, and

thereby control the degree of oxidation in preoxidizer I: and also tosome extent control the temperature of the air entering tower I1. Ipreier to oxidize the melt in tower I! to approximately the solubilityof the oxychloride and copper oxide in the melt. This amounts to 1 to 8mole percent of the total copper salt or approximately 3' to 30% of thetotal conversion of cuprous chloride to cupric chloride per pass throughthe oxidation zones.

The oxygen enriched melt becomes cooled somewhat as it passes throughtower i2 due to contact with cold air and limited extent of oxidationtherein, and hence cooler It! may not be necessary for cooling the meltas it leaves tower I 2 through line 20 in which case the valve in bypassline 2| is opened and the valve in line 20 is closed whereby melt issent directly to the oxidizer-neutralizer tower II. In case cooler I9 isused, the hot melt may be beat exchanged with hydrocarbon feed tochlorinator 24 introduced to cooier i9 through line 25, therebyconserving heat 'of oxidation for use in the chlorine.- tion step. If,on the other hand, it is desirable to remove heat from the system,cooling fluid may be introduced to cooler is via lines 3! and 25 andremoved from cooler I9 via lines 00 and 32.

In packed tower H the heated melt is contacted with heated air leavingtower I! through line l5 and introduced to tower I! at a multiplicity ofpoints through valved lines I611, I61) and lie. Hydrogen chloride inamounts of about four moles per mole of total oxygen absorbed by themelt, in the form of hydrochloric acid of at least 20% concentration butpreferably more concentrated, in a hydrogen chloride equivalentquantity, is introduced at a multiplicity of points near the bottom oftower I! through line 34 provided with a conventional compressor. Themixture of rising air and hydrogen chloride react with the descendingmelt to produce at the tower exit a melt of maximum cupric chloridecontent.

As stated above, the melt issuing from the preoxidizer I2 is saturatedwith respect to oxide content of the melt which progressively diminishesin passing down through tower I! as increased concentration of hydrogenchloride is encountered by the melt. The oxide content is finallydiminished to a very low value at the bottom of reaction tower I! in thezone of highest hydrogen chloride concentration. This condition preventscontamination of the chlorinated product with water vapor formed byneutralization. The water vapor is eliminated from tower I! along withthe oxygen depleted air through line 35. The temperature of the melt intower ll ranges from a maximum of 375 C. at the top of the tower to arange of 425 C. to 525 C. as the melt leaves the tower through line 36leading to the top of chlorination tower 24. If desired, the melt may beheated by any suitable means, as by a furnace (not shown), after leavingtower I1 via line 36, before introduction to chlorination tower 24. Lossof HCl in the overhead via line 35 from tower I1 is minimized bypreconversion of cuprous chloride in the melt in tower l2 to theoxychloride which absorbs any excess hydrogen chloride reaching the topof tower II. If desired, the traces of HCl and volatilized melt lossthrough line 35 may be recovered by condensing a small fraction, forexample, 2 or 3 percent of the steam in the eiliuent stream by means ofa chilled packed tower (not shown).

product from tower 24 in exchanger M.

the condensate being returned through the HO] feed line 34. Thiseilluent stream may also be used for preheating the methane feed totower M or as a source of additional heat or power. The operation intower i is preferably carried out at pressures in excess of atmospheric.though preferably at somewhat lower than the operating pressure ofpreoxidation tower 12.

In packed tower 24 the melt, rich in cupric chloride, contactscountercurrently methane vanors introduced at the bottom of the towervia line 25, compressor 31 and valved line 38 and is thereby convertedto a cuprous chloride rich melt with simultaneous formation oi! amixture oi chloromethanes, predominantly methyl chloride.

By proper adjustment of the valves in lines 5%,

39, iii. 3| and 82 the methane teed to chlorination tower 24 may be usedas a cooling means 1 for preoxidized melt in cooler l9, or the methanemay be used as cooling means for overhead The temperature of the melt inchlorination tower 24 will vary from a range of 425 C. to 525 C. at thetop of the tower to 375 C. to 425 C. at the exit from the tower in line42 depending on the extent of preheating of the methane feed. Thepressure maintained in tower M is usually somewhat less thanthe-pressure in tower ll. Superatmospheric pressures are preferredalthough tower 24 may be operated at atmospheric pressure. The productsof the reaction of the hydrocarbon with the cupric chloride melt intower M are chiefly the chlorolnvdrocarbons such as chloromethanes andhydrogen chloride a mixture of which products is taken overhead via line33 to a fractionation system for further processing. In tower 24 themeltis converted from a. high content of cupric-low content cuprouschloride melt to a low cupric chloride-high cuprous. chloride melt whichis recycled to preoxidation tower i2 via lines 42 and i and pump ii. Iprefer to maintain a liquid level of melt in towers l2, l1 and 26 whichI accomplish by means of float control valves in lines 20, 36 and WhileI have described anessentially adiabatic process for making chlorinatedhydrocarbons utilizing my copper chloride-potassium chloride melts in amanner to obtain improved oxidation rates and hence, reduced size atoxygen absorber, I do not wish to be limited to such use of the meltssince they can be used with equal advantage in an analogous process forthe production of free chlorine, for the production of iree oxygen, orfor the oxidation of organic materials or in any process in which aliquid or carrier adsorbed melt is used. to absorb oxygen.

The foregoing description has been made rather detailed for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, but the appended claim should be construed as broadly aspermissible in view of the prior art.

I claim:

A composition of matter consisting essentially of a melt of potassiumchloride. cuprous chloride and cupric chloride said potassium chloridebe ing present in amounts within the range of from about mole percent toabout 45 mole percent; said cuprous chloride being present in amountswithin the range oi irom about 5 mole percent to about mole percent andsaid cupric chloride being present in amounts within the range of fromabout 10 mole percent to about so mole percent.

CELESTE M. FONIANA.

REWENCES errw The following references are of record in the file of thispatent:

UNITED STATES PATENTS Name Date Grosvenor July 2, 194A) Thomas -m Apr,21, 19%

PATMWERS Gountry Date Great Britain 1866 Great Britain Apr. 14, 1924Germany June 3, 1906 0m REFERENCES Number Number

